Homogeneous mesoporous nanoenergetic metal oxide composites and fabrication thereof

ABSTRACT

The invention provides homogeneous mesoporous metal oxide nanoenergetic composites. A composite of the invention has a regular and uniform nanostructure of metal oxide, which is structured by a surfactant. Metal fuel nanoparticles are homogenously distributed through the regular and uniform nanostructure. The invention further provides methods for making homogeneous metal oxide nanoenergetic composites. A method of the invention forms a metal oxide nanostructure via a sol-gel process with surfactant templating. Metal nanoparticles into the metal oxide nanostructure via wet impregnation.

PRIORITY CLAIM AND REFERENCE TO RELATED APPLICATION

The application claims priority under 35 U.S.C. §119 from priorprovisional application Ser. No. 60/874,177, which was filed on Dec. 11,2006.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with government support under Contract Numberawarded by W15QKN-06-D-0031 awarded by the Department of Defense. Thegovernment has certain rights in the invention.

FIELD

A field of the invention is nanoenergetic materials. Exampleapplications of the invention include military, mining, demolition,detonation devices, fuses, smart ammunitions, propellant initiators,propellant systems, biomedical devices and power generation devices.

BACKGROUND

Energetic materials store significant chemical energy that can bereleased to provide energy for a wide range of purposes. Typical uses ofenergetic materials include as propellants, explosives, and fuels.Nanoenergetic composites take advantage of the high surface area ratiosof nanoparticles to enhance the mass transfer process and rate of energyrelease in the self-sustaining fuel-oxidizer energetic materialsreaction. Reducing the fuel and oxidizer grains physically to thenanoparticle regime minimizes mass transfer effects.

Sol-gel processes are wet-chemical process used for the fabrication ofmetal oxides and other materials from a chemical solution that reactswith another precursor to produce a colloid of nanometer or micrometerscaled particles dispersed in a solvent (sol), which proceeds to form aninorganic network containing a liquid phase (gel). The precursor solventcan be deposited or cast into a desired film or into a container thatdefines a shape prior to the formation of the gel phase. Metal oxideinvolves are formed by connecting metal particles with oxygen (M-O-M) orhydroxide (M-OH-M) bridges. Drying removes the liquid phase from thegel, which can be post-processed to enhance mechanical properties of thematerial.

A sol-gel approach for nanoenergetic composites has been described is byresearchers at Lawrence Livermore National Laboratories. See, Clappsdaleet al, “Synthesis and Characterization of Mixed Metal OxideNanocomposite Energetic Materials,” UCRL-PROC-204118, InternationalPyrotechnics Seminar Fort Collins, Colo., Jul. 12, 2004 through Jul. 16,2004. The materials described include metal oxide/silicon oxidenanocomposites in which the metal oxide is the major component. A fuelmetal, such as aluminum, is incorporated into the metal oxide/siliconoxide matrix to form energetic materials that are based on thermitereactions. Example metal oxides are tungsten trioxide and iron(III)oxide. The paper describes a sol±gel approach in order to manufacturethe thermite composites. Though the use of porous iron oxide preparedusing sol-gel technique in nanoenergetic application is well-known andits preparation has been expounded earlier by other researchers eitherby using sol-gel technique, the prior techniques result only in theformation of disordered porous structure.

Typical known methods of preparing copper oxide nanoparticles preparethe nanoparticles directly from copper ethoxide. This is an expensivematerial that is not readily available in commercial quantities.

SUMMARY OF THE INVENTION

The invention provides homogeneous mesoporous metal oxide nanoenergeticcomposites. A composite of the invention has a regular and uniformnanostructure of metal oxide, which is ordered by a surfactant. Metalfuel nanoparticles are homogenously distributed through the regular anduniform nanostructure. The invention further provides methods for makinghomogeneous metal oxide nanoenergetic composites. A method of theinvention forms a metal oxide nanostructure via a sol-gel process withsurfactant templating. Metal nanoparticles into the metal oxidenanostructure via wet impregnation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the FTIR absorbance spectra of a uniformly structuredhomogenous nanoenergetic mesoporous iron oxide nanocomposite of theinvention (mesoporous Fe₂O₃ powder homogeneously loaded with varyingpercent of AAMCAB);

FIG. 2 is a plot of combustion speed as a function of polymer loading ina uniformly structured homogenous nanoenergetic nanporous iron oxidematrix;

FIG. 3 is a plot of peak pressure measured in reactivity as a functionof polymer loading in a uniformly structured homogenous nanoenergeticmesoporous iron oxide matrix;

FIG. 4 is a plot of reactivity measured as a function of polymer loadingin a uniformly structured homogenous mesoporous iron oxide matrix;

FIG. 5 is a plot of typical data obtained from simultaneous measurementsof combustion wave speed (R) and pressure measurements for a uniformlystructured homogenous nanoenergetic iron oxide composite (Fe₂O₃+10%AAMCAB)+Al(120 nm);

FIG. 6 plots the dependence of burn rate R on pressure P for uniformlystructured homogenous nanoenergetic composites of (Fe₂O₃+10%AAMCAB)+Al(120 nm);

FIG. 7 plots burn rate as a function of surfactant concentration used inthe preparation of uniformly structured homogenous nanoenergetic CuO.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention provides homogeneous mesoporous metal oxide nanoenergeticcomposites. A composite of the invention has a regular and uniformnanostructure of metal oxide, which is ordered by a surfactant. Metalfuel nanoparticles are homogenously distributed through the regular anduniform nanostructure. The invention further provides methods for makinghomogeneous metal oxide nanoenergetic composite. A method of theinvention forms a metal oxide nanostructure via a sol-gel process withsurfactant templating. Metal nanoparticles are introduced into the metaloxide nanostructure via wet impregnation in a self-assembly process.

The present invention provides energetic nanocomposites having a highlyuniform structure with metal fuel homogeneously distributed throughout ametal oxide oxidizer nanostructure. Preferred embodiment energeticnanocomposites have a regular and uniformly sized porosity and areprepared by a surfactant template method of making the same. Otherpreferred embodiment energetic nanocomposites have regular and uniformlysized nanorod structures with fuel metal particles homogeneouslydistributed through the structure Embodiments of the invention provideiron oxide (Fe₂O₃) based energetic nanocomposites and porous copperoxide (CuO) nanoparticle based energetic nanocomposites.

Methods of the invention provide for the formation of uniformlystructured metal oxides that are homogenous. The surfactant templatingproduces a high level of homogeneity because of the well-definedmicellar size of the surfactant impregnated with polymer surfactant andfuel particles for resultant homogenous nanoenergetic metal oxidecomposites. Methods of the invention, and accordingly the resultanthomogenous nanoenergetic metal oxide composites, can be tuned to achievedifferent combustion characteristics, e.g., combustion speed, pressure,reactivity etc.

In a preferred fabrication method of the invention regular and uniformlymesoporous metal oxide nanocomposite is made using a surfactant templatemethod via sol gel processing with fuel nanoparticles impregnated andhomogeneously distributed into the regular and uniformly mesoporousmetal oxide, which is preferably Fe₂O₃ or CuO. The homogeneousdistribution of oxidizer and fuel in nanocomposites of the inventionprovides high rates of energy release.

Preferred fabrication methods of the invention provide for thepreparation of ordered energetic nanocomposites with low-cost materialsand techniques that are suitable for commercial scale fabrication. Apreferred embodiment method of preparing uniformly structurednanoenergetic mesoporous CuO utilizes relatively low-cost precursormaterial. In a preferred embodiment, copper oxide nanoparticles are madeby first forming a gel of copper hydroxide from a mixture of a copperchloride solution and a surfactant diluted in a solvent. The gel is nexttreated with solvents to remove impurities. Finally, the gel is calcinedat controlled temperatures to form the copper oxide nanoparticles. Useof the copper chloride starting material greatly reduces the cost ofgenerating the nanooxidizer compared to techniques that form copperoxide nanoparticles directly from a copper ethoxide precursor. Underexemplary experimental conditions used to test the present invention,nanoparticles with a size range of about 50-100 nm having ordered poreswere produced. Copper chloride is readily available in commercialquantities. With the fabrication method of the invention, the exact sizeand shape of the copper oxide nanoparticle is tunable through dilutionof the surfactant used to make it.

A preferred embodiment method of preparing uniformly structuredhomogenous nanoenergetic mesoporous iron oxide composites similarly usesa combination of sol-gel chemistry and surfactant template approach. Ina preferred method an iron oxide (Fe₂O₃) gel with ordered mesoporousstructure is synthesized using a combination of sol-gel processing andsurfactant templating approach. The resultant structured porous Fe₂O₃particles are modified by incorporating a gas generating polymer using awet impregnation technique. The amount of polymer can be adjusted toproduce homogenous nanoenergetic metal oxide composite with differentcharacteristics. A particularly preferred embodiment mixes modifiedoxidizer particles with Al nanoparticles at an optimum equivalence ratioof 1:4 to form the nanoenergetic composites. The combustioncharacteristics such as reactivity, combustion speed and pressure aredetermined as a function of polymer composition. Incorporation ofadditional polymers into the pores of oxidizer matrix reduces the burnrate (combustion wavespeed) while enhancing the pressure generatedduring the energetic reaction. The presence of more polymers in theoxidizer matrix leads to sustained pressure over a longer period of timefacilitating their use in propellant applications. On the other hand, byreducing the polymer in the porous structure, the combustion wave speedincreases significantly making the nanocomposite sell-suited forenhanced blast applications.

In preferred embodiment homogenous nanoenergetic metal oxide composites,the Electrostatic Discharge sensitivity of Al nanoparticles in thecomposites is reduced. Details of preferred methods for reducing theelectrostatic discharge are disclosed in the application entitledReducing Electrostatic Discharge Ignition Sensitivity of MIC Materials,filed on the same date as the present application, awarded Ser. No.______, which application claims priority from provisional applicationserial number 60,874,089. In preferred embodiments, Al nanoparticles arecoated with perfluorooctal mono-functional trimethoxysilane (FSM) as amolecular linker layer and then an energetic polymer and then mixed withmetal oxides to reduce the sensitivity of the nanoenergetic composites.

Preferred embodiments of the invention will now be discussed withrespect to the drawings. The drawings may include schematicrepresentations, which will be understood by artisans in view of thegeneral knowledge in the art and the description that follows. Preferredembodiments will be discussed with respect to experimental examplenanocomposites and methods of fabrication, while artisans willappreciate the broader commercial applications and scale-ups of theexperiments that are within the scope of the invention.

General steps for forming uniformly structured homogenous nanoenergeticcomposites of preferred embodiments involve forming a uniformlystructured oxidizer by sol gel surfactant template processing and thenintroducing a fuel into the oxidizer structure, which achieves thehomogeneous composite. The formation of the oxidizer with surfactanttemplating according to preferred embodiments relies upon self-assemblyof surfactant micelles. Above a certain concentration of surfactantsknown as the critical micellar concentration (CMC), surfactant micellesself-assemble in a solution and produce a template with uniform micellesdistribution. When inorganic oxidizer precursor is introduced in thesolution, hydrolysis reaction takes place around the micelles and thegelation takes place subsequently (after the gelling agent (Typicallypropylene oxide (PPO)) is added. Other gelling agents include, forexample, cyclic ethers, and hydroxide salts. Removal of the surfactanttemplate leaves behind the imprints of inorganic oxidizer network withpores in place of surfactant micelles. Therefore, by using surfactanttemplating and sol-gel methods, an oxidizer with ordered poredistribution and uniform pore sizes is readily achieved. The oxidizercan be homogeneously impregnated with fuel to complete the composite.

Surfactant templating agents permit the homogenous impregnation of thefuel atoms into the oxidizer network. This ensures homogeneous mixing ofthe fuel atoms with the oxidizer thus increasing the energy content andthe energy release rate. Mesopores can be tailored based on the size ofsurfactant molecules. The hot-spot density can be controlled usingimpregnation techniques. Nanorod size also can be increased based onsurfactant molecules so that more Al-nanoparticles can be assembled.

A preferred embodiment homogeneous mesoporous metal oxide nanoenergeticcomposite has a regular and uniform mesoporous nanostructure of metaloxide. Surfactant provides the regular and uniform nanostructure. Metalfuel nanoparticles are homogenously distributed through the regular anduniform nanostructure. In a preferred embodiment, the regular anduniform nanostructure is mesoporous iron oxide nanoparticles, and thecomposite also includes a gas generating polymer homogenouslydistributed throughout the regular and uniform nanostructure. Apreferred gas generating polymer is Acrylamidomethyl cellulose acetatebutyrate (AAMCAB) and a preferred surfactant is Brij 76. Generally, thegas generating polymer should be a polymer having several carbon,nitrogen, hydrogen and oxygen atoms.

In another embodiment, the regular and uniform nanostructure ismesoporous iron oxide nanorods, A preferred surfactant for themesoporous nanorods is CTAB (cetyl trimethylammonium bromide.

In another preferred embodiment, the regular and uniform nanostructurecomprises mesoporous CuO. For the CuO wherein the surfactant ispreferably Pluronics (P123).

A preferred method for making homogeneous metal oxide nanoenergeticcomposite involves forming a metal oxide nanostructure via a sol-gelprocess with surfactant templating and introducing metal nanoparticlesinto the metal oxide nanostructure via wet impregnation. In a preferredmethod where the metal oxide comprises CuO, the method includes steps ofpreparing a surfactant solution of a surfactant in a solvent; dissolvinga water-soluble copper compound in water; diluting the surfactantsolution to make nanoparticles of the desired size and shape; combiningthe diluted surfactant solution with the dissolved copper compound tomake a liquid mixture; sonicating the liquid mixture; adding gellingagent to the liquid mixture; vigorously agitating the liquid mixtureprior to formation of copper hydroxide gel; allowing the copperhydroxide gel to form; aging the copper hydroxide gel; washing thecopper hydroxide gel in ethanol; and calcining the copper hydroxide gelto form the metal oxide nanostructure. The step of forming preferablyincludes reacting metal salts in solution; adjusting the pH of thesolution; heating the solution to obtain a precipitate; purifying anddrying the precipitate to obtain a powder; and calcinating the powder toobtain the metal oxide nanostructure.

In a preferred embodiment gelling agent comprises a hydroxide salt

In a preferred embodiment the precursor solution comprises analcohol-soluble copper salt dissolved in alcohol.

Homogeneous Fe₇O₃ Oxidizers and Composites

Mesoporous Oxidizer and Composites

A first experiment involved the production of uniformly structuredmesoporous iron oxide as an oxidizer for a uniformly structuredhomogenous nanoenergetic mesoporous iron oxide composite of theinvention. The experiment used laboratory equipment and was conducted ona laboratory scale, while artisans will recognize that other equipmentand corresponding techniques would be used in a commercial fabricationprocess based upon the example experimental embodiment.

In one beaker, 0.357 g of Brij 76 (non-ionic surfactant from Sigma

Aldrich) was dissolved in 15 ml of absolute ethanol. The solution washeated to 60° C. and maintained for 15 minutes under constant stirring.This solution was referred as solution A. In another beaker, 5.0 g ofFe(NO₃)₃.9H₂O was dissolved in 27.5 ml of absolute ethanol. Thissolution (Solution B) was placed in a sonicator bath for about 10minutes to ensure complete dissolution of the salt in ethanol. SolutionB was slowly added to solution A under gentle stirring and the resultantsolution mixture was then placed in a sonication bath for 10 minutes. Tothis solution mixture, 25.9 ml of the propylene oxide (Sigma Aldrich,St. Louis) was added under constant stirring. On addition of propyleneoxide, the solution was transformed into a gel of FeOOH(Fe-oxyhydroxide) in 1-2 min.

FeOOH gel was further processed to remove impurities by treating withacidified ethanol. In this treatment, the gel were first soaked inethanol for 48 h at 60° C. and later annealed at 200° C. for 6 h. Duringcalcination, FeOOH was converted into Fe₂O₃. A few gel samples were alsotreated with supercritical CO₂ at 80° C. and 7000 psi for 24 h to removeimpurities. Impurity removal was confirmed by FTIR (Fourier TransformInfrared Spectroscopy) analysis. The synthesized ordered mesoporousFe₂O₃ product was revealed by TEM (transmission electron microscopy)images, which clearly showed the formation of ordered poreshomogeneously distributed throughout the matrix with a pore size of 5-10nm.

The dried ordered porous iron oxide powder was then loaded withdifferent weight percent of a polymer, (Acrylamidomethyl) celluloseacetate butyrate (AAMCAB) (CAS number: 97635-64-8 Sigma Aldrich, SaintLouis, Mo.) using a wet impregnation method. It was first dissolved inacetone to prepare a solution of 5-20% (wt. %). To this solution, Fe₂O₃powder was added and treated in an ultrasonic bath for 2 hours and leftundisturbed for 12 hours. After that, the mixture was dried at 80° C. toremove the solvent. Successful infiltration of the AAMCAB polymer wasmonitored with Fourier transform infrared spectroscopy. FIG. 1 shows theFTIR absorbance spectra of mesoporous Fe₂O₃ powder homogeneously loadedwith varying percent of AAMCAB. The inset of FIG. 1 shows the FTIRspectrum of AAMCAB polymer.

Specifically, FIG. 1 shows FTIR absorbance spectra of Fe₂O₃ and AAMCABloaded with different amounts (5, 10 and 15%) of Fe₂O₃. For reference,absorbance spectrum of AAMCAB is also shown in inset of FIG. 1.Characteristic vibrations of AAMCAB observed at 1000-1300 cm⁻¹,1375-1450 cm⁻¹, 1745 cm⁻¹, 2800-3000 cm⁻¹ and 3200-3550 cm⁻¹ areattributed to C—O stretch of C—O—C group present in the aromatic ring,CH_(n) (n=2 or 3) bending mode, C═O stretch, CH_(n) stretching mode andO—H stretch respectively.

The bands observed at 460 cm⁻¹ and 535 cm⁻¹ are assigned to the Fe—Ovibrations. A comparison of the absorbance spectra of AAMCAB loadedFe₂O₃ (main figure) with that of AAMCAB alone (inset) indicates theinfiltration of the polymer into the porous matrix of Fe₂O₃.Furthermore, with increasing amount of AAMCAB loading, the intensity ofthe characteristic peaks at 1000-1300 cm⁻¹, 1375-1450 cm⁻¹, 1745 cm⁻¹,2800-3000 cm⁻¹ increase.

Typical preparation of nanoenergetic mixtures containing gas generatingpolymer (AAMCAB) loaded Fe₂O₃ as oxidizer with homogenous fueldistribution was as follows. Accurately weighed 0.2 g of oxidizer wasmixed with 0.094 g of Al-nanoparticles in 2-propanol using ultrasonicbath for 6-8 hrs. When the infiltrated polymers are burnt during thehigh temperature thermite reaction, more gas is produced therebyincreasing the generated pressure. To achieve this, AAMCAB was selectedas it has several carbon and nitrogen atoms, which would combine withoxygen to produce gases on combustion. Also this polymer decomposes intoseveral gaseous products contributing to higher pressure. Moreover,AAMCAB (Sigma Aldrich) has glass transition temperature of 118 C withdensity of 1.31 g/cc at 25° C. and it is completely soluble in solventssuch as acetone, butanone etc. Generally, polymers that provide one ormore of these attributes are preferred as a gas generating polymer.

Combustion characteristics such as combustion speed and reactivitymeasured in terms of the rate of pressure generated during the thermitereaction were determined as a function of the amount of polymer loadingand as a function of Al particle size. The combustion speed was measuredusing an optical method, wherein a combination of a Tektronix TDS460AFour Channel Digital Oscilloscope (100 MHz maximum bandwidth),photodiodes and fiber optics were used. In some tests, two oscilloscopesand up to 8 recorded channels were used. A transparent Lexane tube (95mm long, 9 mm OD and 3.2 mm ID) was filled with 200 mg of nanoenergeticmixture. The powder filled approximately half of the tube cross section.Combustion experiments were performed in a confined geometry with bothends of the Lexane tube being closed. Initiation spark was located atthe left side of the tube and a pressure sensor was at the opposite end.The reaction front position was determined by properly setting (up toseven) the collimated photodiodes, located along the test tube with 10mm spacing interval. The combustion speed along the tube was obtainedfrom recorded time-arrival data.

Reactivity rate tests were performed in a closed volume using a typicalmass of 20 mg in a metal-well of 6.2 mm in diameter and 2 mm depth witha packing density of 0.33 g/cm³. A Ni-alloy fuse wire d=0.13 mm was usedfor ignition of the nanothermite material. The pressure inside milliwellwas monitored by a piezoelectric pressure sensor (PCB Piezotronics Model119B12) with a maximum pressure range of 827 MPa.

Data was obtained through the experiments to demonstrate that thecombustion characteristics of uniformly structured homogenousnanoenergetic composites of the invention can be predetermined andselected during fabrication. The characteristics are tunable. Theresults are shown in FIGS. 2-4. FIG. 2 is a plot of combustion speed asa function of polymer homogeneous loading in an ordered porous ironoxide matrix. FIG. 3 is a plot of peak pressure measured in reactivityas a function of polymer loading. FIG. 4 is a plot of reactivitymeasured as a function of polymer loading in porous iron oxide matrix.The data show that combustion speed and reactivity goes down while thepeak pressure increases with increasing polymer loading.

Combustion wave speed and pressure measurements were also madesimultaneously. FIG. 5 shows typical data obtained from simultaneousmeasurements of combustion wave speed (R) and pressure measurements fora uniformly structured homogenous nanoenergetic iron oxide composite(Fe₂O₃+10% AAMCAB)+Al (120 nm) The percentage here refers to the amountof AAMCAB used with respect to the amount of iron oxide during thepreparation of the polymer loading into porous matrix process. Thepercentage is not measured after the preparation. However, with the FTIRspectra show gradual increase in the intensity of specific peaks ofAAMCAB with increasing amounts of AAMCAB used in the preparation. Thissimultaneous measurement permits plotting of the dependence of R (m/sec)on pressure P (MPa) for subsonic regime, as shown in FIG. 6. Theobtained data was fitted to a power law dependence for ballisticpropellant, also well known as Vieille's law,

R=βP^(α)

where: β (m/(sec-MPa)) and α (dimensionless) refer to experimentalconstants. Specifically, the magnitude of the pressure exponent isrequired to be small in order to avoid transition to unstable burning athigh pressures. FIG. 6 plots the dependence of R on P for the uniformlystructured homogenous nanoenergetic composite of (Fe₂O₃+10% AAMCAB)+Al.The plot fits the power law approximately with coefficients in Vieille'sequation as follows:

R=552*P ^(0.408)

The exponent 0.408 corresponds to the propellant material. Thecoefficient 552 is high because of the high value of combustion wavespeed of nanothermites. This can be reduced by introducing more gasgenerating polymer Small value of exponential slope α=0.408 shows thatcombustion of our nanoenergetic material (Fe₂O₃+10% AAMCAB)+Al is stableunder high pressures and have small dependence on pressure. Tests haveshown that the burn rate of the thermite materials have strongdependence on the composition rather than on pressure. This propertypermits the nanoenergetic composite for both propellant and enhancedblast applications.

Mesoporous Nanorod Fe₂O₃ with Al-nanoparticle Composites

Other experiments prepared mesoporous nanorod oxide structures andcomposites with fuel particles. In this method, iron chloride(FeCl₃.6H₂O) (1.08 g) and 1.0 g of cetyl trimethylammonium bromide(CTAB) were dissolved in 40 ml of de-ionized water and sonicated for ½ hto ensure complete dissolution. The resultant mixture was autoclaved for12 hrs at 80° C. The yellow colored precipitate obtained was stirred inethanol for 12 h to remove the surfactant. The yellow product (FeOOH)was repeatedly washed with water to remove the impurities dried at 100°C. to get a dry powder. The dried powder was pulverized in a mortar andcalcined at 520° C. for 4 hrs to obtain porous iron oxide nanorods. Alnanoparticles can be self-assembled on and in the mesoporous nanorods asdescribed above.

Homogeneous Mesoporous CuO Oxidizer/Combined Oxidizer and Composites:

Experiments were also conducted to synthesize and test uniformlystructured homogenous nanoenergetic CuO oxides and composites. PorousCuO nanoparticles were prepared using surfactant templating with lowcost precursors. The CuO oxides are formed by first preparing a copperchloride and surfactant solution in a solvent. Propylene oxide is addedto induce gelation. The gel is next treated with solvents to removeimpurities. The gel is calcined at controlled temperatures to form thecopper oxide uniformly structured homogenous nanoenergetic composite.Then, the porous CuO was mixed with Al nanoparticles as fuel and thecombustion wave velocity was determined for samples prepared varying thesurfactant concentration.

Similar to the preparation for the iron oxide composites describedabove, porous CuO nanoparticles was synthesized using a surfactanttemplate approach and then Al-nanoparticles were mixed with the oxidizerto form the energetic composite. Specifically, in solution A, 0.75 g ofcopper chloride (Sigma Aldrich, St. Louis) was first dissolved in DIwater. A stock solution of 40 wt. % of Pluronics, P123, (BASFCorporation) in ethanol was prepared separately.

Pore size and shape can be tuned by varying the concentration of thesurfactant used in the synthesis. To vary the surfactant concentration,the stock solution was diluted appropriately. For example, to prepareporous CuO with 10% P123 solution, the stock solution of 40 wt. % wasdiluted to four times and added to solution A. The mixture was sonicatedfor 10 minutes. About 2.5 mL of propylene oxide was added to thismixture and then shaken vigorously immediately before the formation ofcopper hydroxide gel begins.

The gel is aged, typically for 24-48 hours. The gel is then washedthoroughly with ethanol through stirring for 24 hours to remove theimpurities. The samples were then calcined to 450° C. in a controlledmanner using a programmable furnace. Impurity removal and formation ofcopper oxide (CuO) was confirmed by FTIR analysis.

TEM was used to investigate the morphology of the CuO. The TEM imagesrevealed formation of CuO nanoparticles with uniform size and shape. Theaverage size of the nanoparticle is about 100 nm. The detailedmicrostructure of one such particle recorded at a higher magnificationreveals the porous morphology of the nanoparticle. The pore size isabout 3-4 nm for CuO nanoparticles prepared with 8 wt. %. P123.Optimization of the process parameters permits tunable pore size andshape to be realized and optimized enhanced energetic properties to beachieved.

Fuel was then introduced into the CuO homogenous oxide. Typically 200 mgof CuO oxidizer nanoparticles were mixed with 85 mg of Al fuelnanoparticles and the mixture was sonicated in a sonic bath (ColeParmer) for 4 hours to realize homogeneous mixing of oxidizer and fuelnanoparticles. The slurry obtained was then dried and the energeticcomposite was thus obtained. The performance of the energetic compositewas tested by measuring the burn rate.

The burn rate was measured for all samples and monitored as a functionof P123 surfactant concentration used in the preparation of CuOnanoparticle composite. FIG. 7 plots burn rate as a function ofsurfactant concentration used in the preparation of uniformly structuredhomogenous nanoenergetic CuO. It is clear that the burn rate can betuned from 800-1850 m/s by simply varying the P123 concentration and thehigh burn rate of 1850 m/s was obtained in case of sample prepared with8 wt. % of P123. The process can be adjusted to to achieve CuO basedmesoporous energetic composites with tailored combustioncharacteristics.

While specific embodiments of the present invention have been shown anddescribed, it should be understood that other modifications,substitutions and alternatives are apparent to one of ordinary skill inthe art. Such modifications, substitutions and alternatives can be madewithout departing from the spirit and scope of the invention, whichshould be determined from the appended claims.

Various features of the invention are set forth in the appended claims.

1. A homogeneous metal oxide nanoenergetic composite, the compositecomprising: a regular and uniform mesoporous nanostructure of metaloxide; surfactant providing the regular and uniform nanostructure; andmetal fuel nanoparticles homogenously distributed through the regularand uniform nanostructure.
 2. The composite of claim 1, wherein theregular and uniform nanostructure comprises mesoporous iron oxidenanoparticles, the composite further comprising a gas generating polymerhomogenously distributed throughout the regular and uniformnanostructure.
 3. The composite of claim 2, wherein the gas generatingis polymer comprises Acrylamidomethyl cellulose acetate butyrate(AAMCAB) and the surfactant comprises Brj
 76. 4. The composite of claim2, wherein the gas generating polymer comprises a soluble polymer havingseveral carbon, nitrogen, hydrogen and oxygen atoms.
 5. The composite ofclaim 1, wherein the regular and uniform nanostructure comprisesmesoporous iron oxide nanorods.
 6. The composite of claim 5, wherein thesurfactant comprises a soluble polymer having several carbon, hydrogenand oxygen atoms.
 7. The composite of claim 5, wherein the surfactantcomprises cetyl trimethylammonium bromide (CTAB).
 8. The composite ofclaim 1, wherein the regular and uniform structure comprises mesoporousiron oxide nanoparticles.
 9. The composite of claim 8, furthercomprising a gas generating polymer impregnated into the orderedmesoporous iron oxide.
 10. The composite of claim 9, wherein the gasgenerating polymer has several carbon, hydrogen, nitrogen and oxygenatoms.
 11. The composite of claim 10, wherein the regular and uniformnanostructure comprises mesoporous CuO.
 12. The composite of claim 11,wherein the surfactant comprises Pluronics (P123).
 13. The composite ofclaim 12, wherein the fuel comprises Al nanoparticles.
 14. The compositeof claim 13, wherein the approximate equivalence ratio of metal oxide toAl is 1.4.
 15. The composite of claim 1, wherein the fuel comprisesmetal nanoparticles that are coated with a molecular linker layer and afluoropolymer.
 16. A method for making homogeneous mesoporous metaloxide nanoenergetic composite, the method comprising: forming a metaloxide nanostructure via a sol-gel process with surfactant templating;and introducing metal nanoparticles into the metal oxide nanostructurevia wet impregnation.
 17. The method of claim 16, wherein the metaloxide nanostructure comprises one of iron oxide or CuO.
 18. The methodof claim 17, wherein said metal oxide comprises CuO, and said step offorming comprises: preparing a surfactant solution of a surfactant in asolvent; dissolving a water-soluble copper compound in water; dilutingthe surfactant solution to make nanoparticles of the desired size andshape; combining the diluted surfactant solution with the dissolvedcopper compound to make a liquid mixture; sonicating the liquid mixture;adding gelling agent to the liquid mixture; vigorously agitating theliquid mixture prior to formation of copper hydroxide gel; allowing thecopper hydroxide gel to form; aging the copper hydroxide gel; washingthe copper hydroxide gel in ethanol; calcining the copper hydroxide gelto form the metal oxide nanostructure.
 19. The method of claim 19,wherein said step of forming comprises: reacting metal salts insolution; adjusting the pH of the solution; heating the solution toobtain a precipitate; purifying and drying the precipitate to obtain apowder; calcinating the powder to obtain the metal oxide nanostructure.20. The method of claim 19, wherein the precursor solution comprises analcohol-soluble copper salt dissolved in alcohol.